sdk/2.1/docs/man/xhtml/global.html - external/github.com/KhronosGroup/OpenCL-Registry - Git at Google

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       <div xmlns="" class="refnamediv">
         <a xmlns="http://www.w3.org/1999/xhtml" id="__global"></a>
         <h1>__global</h1>
         <p>
             Address space qualifier.
         </p>
       </div>
       <div class="refsect2">
         <a id="synopsis"></a>
         <h3>
         </h3>
         <div class="informaltable">
           <table class="informaltable" border="0">
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                 <td align="left">
 __global
 global
                         </td>
               </tr>
             </tbody>
           </table>
         </div>
       </div>
       <div class="refsect1">
         <a id="description"></a>
         <h2>Description</h2>
         <p>
             The <code class="function">__global</code> or <code class="function">global</code> address
             space name is used to refer to memory objects (buffer or image objects)
             allocated from the global memory pool.
         </p>
         <p>
             A buffer memory object can be declared as a pointer to a scalar, vector
             or user-defined struct. This allows the kernel to read and/or write any
             location in the buffer.
         </p>
         <p>
             The actual size of the array memory object is determined when the memory
             object is allocated via appropriate API calls in the host code.
         </p>
         <p>
             As image objects are always allocated from the global
             address space, the <code class="function">__global</code> or
             <code class="function">global</code> qualifier should not be
             specified for image types. The elements of an image object
             cannot be directly accessed. Built-in functions to
             read from and write to an image object are
             provided.
         </p>
         <p>
             Variables defined at program scope and static
             variables inside a function can also be declared
             in the <code class="function">global</code> address space.
             They can be defined with any valid OpenCL C data type except
             for those in table 6.3. In particular, such
             program scope variables may be of any user-defined
             type, or a pointer to a user-defined type. In
             the presence of shared virtual memory, these pointers
             or pointer members should work as expected as
             long as they are shared virtual memory pointers
             and the referenced storage has been mapped appropriately.
             These variables in the <code class="function">global</code>
             address space have the same lifetime as the program,
             and their values persist between calls to
             any of the kernels in the program. These variables
             are not shared across devices. They have
             distinct storage.
         </p>
         <p>
             Program scope and static variables in the
             <code class="function">global</code> address space may be initialized, but only
             with constant expressions.
         </p>
         <p>
             The <code class="code">const</code> qualifier can also be used
             with the <code class="function">__global</code> qualifier to
             specify a read-only buffer memory object.
         </p>
       </div>
       <div class="refsect1">
         <a id="notes"></a>
         <h2>Notes</h2>
         <h4><a id="id-1.6.2"></a>General information about address space qualifiers</h4>
         <p>
       OpenCL implements the following disjoint named address
       spaces: <code class="function">__global</code>,
       <code class="function">__local</code>, <code class="function">__constant</code>, and
       <code class="function">__private</code>. The address space qualifier may be used in variable
       declarations to specify the region of memory that is used to allocate the object. The
       C syntax for type qualifiers is extended in OpenCL
       to include an address space name as a valid type qualifier.
       If the type of an object is qualified by an address
       space name, the object is allocated in the
       specified address name; otherwise, the object is
       allocated in the generic address space.
     </p>
         <p>
       The address space names without the  __  prefix i.e. <code class="function">global</code>,
       <code class="function">local</code>, <code class="function">constant</code>
       and <code class="function">private</code>
       may be substituted for the corresponding address
       space names with the  __  prefix.
     </p>
         <p>
         The address space name for arguments to a function
         in a program, or local variables of a function
         is <code class="function">__private</code>. All function
         arguments shall be in the <code class="function">__private</code> address space.
         The address space for a variable at program scope
         or a static variable inside a function can either
         be <code class="function">__global</code> or
         <code class="function">__constant</code>, but defaults to
         <code class="function">__global</code> if not specified.
     </p>
         <p>
         OpenCL 2.0 adds support for an unnamed <code class="function">generic</code>
         address space. Pointers that are declared
         without pointing to a named address space point to the
         <code class="function">generic</code> address space. Before
         referring to the region pointed to, the pointer
         must be associated with a named address space.
         Functions may be written with arguments and return values that point to the
         <code class="function">generic</code> address space.
     </p>
         <p>
         kernel function arguments declared to be a pointer or
         an array of a type must point to one of
         the named address spaces <code class="function">__global</code>,
         <code class="function">__local</code> or <code class="function">__constant</code>.
     </p>
         <p>
         The named address spaces are a subset of the generic
         address space except for the <code class="function">constant</code>
         address space.
     </p>
         <p>
         A pointer to address space A can only be assigned to
         a pointer to the same address space A or a
         pointer to the <code class="function">generic</code> address
         space. Casting a pointer to address space A to a pointer to
         address space B is illegal if A and B are named
         address spaces and A is not the same as B.
     </p>
         <p>
         The <code class="function">__global</code>, <code class="function">__constant</code>,
         <code class="function">__local</code>,
         <code class="function">__private</code>, <code class="function">__generic</code>,
         <code class="function">global</code>,
         <code class="function">constant</code>, <code class="function">local</code>, and
         <code class="function">private</code> names are reserved for use as address space
         qualifiers and shall not be used otherwise.
         The <code class="function">__generic</code> and <code class="function">generic</code>
         names are reserved for future use.
     </p>
         <p>
         The size of pointers to different address spaces
         may differ. It is not correct to assume
         that, for example, <code class="code">sizeof(__global int *)</code>
         always equals <code class="code">sizeof(__local int *)</code>.
     </p>
       </div>
       <div class="refsect2">
         <a id="example1"></a>
         <h3>
             Examples
         </h3>
         <p>
       General qualifier examples follow:
     </p>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">
 // declares a pointer p in the private address space that
 // points to an object in address space global
 global int *p;

 void foo (...)
 {
     // declares an array of 4 floats in the private address space
     float x[4];
     ...
 }
             </td>
               </tr>
             </tbody>
           </table>
         </div>
         <p>
       Example:
     </p>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">
 private int f() { ... } // should generate an error
 local int *f() { ... } // allowed
 local int * private f() { ... }; // should generate an error.
             </td>
               </tr>
             </tbody>
           </table>
         </div>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">
 global float4  *color;      // An array of float4 elements
 typedef struct {
       float a[3];
       int   b[2];
 } foo_t;
 global foo_t   *my_info;    // An array of foo_t elements.
                         </td>
               </tr>
             </tbody>
           </table>
         </div>
         <p>
         </p>
         <div class="informaltable">
           <table class="informaltable" border="0">
             <colgroup>
               <col align="left" class="col1" />
             </colgroup>
             <tbody>
               <tr>
                 <td align="left">
 global int foo;         // OK.
 int foo;                // OK. Declared in the global address space
 global uchar buf[512];  // OK.
 global int baz = 12;    // OK. Initialization is allowed
 static global int bat;  // OK. Internal linkage

 global uchar bigbuf[CL_DEVICE_MAX_GLOBAL_VARIABLE_SIZE]; // OK.

 static int foo;         // OK. Declared in the global address space
 static global int foo;  // OK.

 int *foo;               // OK. foo is allocated in global address space.
                         // pointer to foo in generic address space

 void func(...)
 {
    int *foo;            // OK. foo is allocated in private address space.
                         // foo points to a location in generic address space.
    ...
 }

 global int * global ptr;          // OK.
 int * global ptr;                 // OK.
 constant int *global ptr=&amp;baz;    // error since baz is in global address
                                   // space.
 global int * constant ptr = &amp;baz; // OK

 // Pointers work. Also, initialization to a constant known at
 // program load time
 global int *global baz_ptr = &amp;baz;

 global image2d_t im;       // Error. Invalid type for program scope
                            // variables

 global event_t ev;   // Error. Invalid type for program scope variables

 global int *bad_ptr; // Error. No implicit address space
                         </td>
               </tr>
             </tbody>
           </table>
         </div>
       </div>
       <div class="refsect1">
         <a id="specification"></a>
         <h2>Specification</h2>
         <p>
             <img src="pdficon_small1.gif" />

             <a href="https://www.khronos.org/registry/cl/specs/opencl-2.1-openclc.pdf#page=34" target="OpenCL Spec">OpenCL Specification</a>
         </p>
       </div>
       <div class="refsect1">
         <a id="seealso"></a>
         <h2>Also see</h2>
         <p>
             <a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>,
             <a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a>,
             <a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</span></span></a>,
             <a class="citerefentry" href="qualifiers.html"><span class="citerefentry"><span class="refentrytitle">qualifiers</span></span></a>
         </p>
       </div>
       <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
 Permission is hereby granted, free of charge, to any person obtaining a
 copy of this software and/or associated documentation files (the
 "Materials"), to deal in the Materials without restriction, including
 without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Materials, and to
 permit persons to whom the Materials are furnished to do so, subject to
 the condition that this copyright notice and permission notice shall be included
 in all copies or substantial portions of the Materials.
 </div>
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	<a xmlns="http://www.w3.org/1999/xhtml" id="__global"></a>
	<h1>__global</h1>
	<p>
	Address space qualifier.
	</p>
	</div>
	<div class="refsect2">
	<a id="synopsis"></a>
	<h3>
	</h3>
	<div class="informaltable">
	<table class="informaltable" border="0">
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	__global
	global
	</td>
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	</div>
	<div class="refsect1">
	<a id="description"></a>
	<h2>Description</h2>
	<p>
	The <code class="function">__global</code> or <code class="function">global</code> address
	space name is used to refer to memory objects (buffer or image objects)
	allocated from the global memory pool.
	</p>
	<p>
	A buffer memory object can be declared as a pointer to a scalar, vector
	or user-defined struct. This allows the kernel to read and/or write any
	location in the buffer.
	</p>
	<p>
	The actual size of the array memory object is determined when the memory
	object is allocated via appropriate API calls in the host code.
	</p>
	<p>
	As image objects are always allocated from the global
	address space, the <code class="function">__global</code> or
	<code class="function">global</code> qualifier should not be
	specified for image types. The elements of an image object
	cannot be directly accessed. Built-in functions to
	read from and write to an image object are
	provided.
	</p>
	<p>
	Variables defined at program scope and static
	variables inside a function can also be declared
	in the <code class="function">global</code> address space.
	They can be defined with any valid OpenCL C data type except
	for those in table 6.3. In particular, such
	program scope variables may be of any user-defined
	type, or a pointer to a user-defined type. In
	the presence of shared virtual memory, these pointers
	or pointer members should work as expected as
	long as they are shared virtual memory pointers
	and the referenced storage has been mapped appropriately.
	These variables in the <code class="function">global</code>
	address space have the same lifetime as the program,
	and their values persist between calls to
	any of the kernels in the program. These variables
	are not shared across devices. They have
	distinct storage.
	</p>
	<p>
	Program scope and static variables in the
	<code class="function">global</code> address space may be initialized, but only
	with constant expressions.
	</p>
	<p>
	The <code class="code">const</code> qualifier can also be used
	with the <code class="function">__global</code> qualifier to
	specify a read-only buffer memory object.
	</p>
	</div>
	<div class="refsect1">
	<a id="notes"></a>
	<h2>Notes</h2>
	<h4><a id="id-1.6.2"></a>General information about address space qualifiers</h4>
	<p>
	OpenCL implements the following disjoint named address
	spaces: <code class="function">__global</code>,
	<code class="function">__local</code>, <code class="function">__constant</code>, and
	<code class="function">__private</code>. The address space qualifier may be used in variable
	declarations to specify the region of memory that is used to allocate the object. The
	C syntax for type qualifiers is extended in OpenCL
	to include an address space name as a valid type qualifier.
	If the type of an object is qualified by an address
	space name, the object is allocated in the
	specified address name; otherwise, the object is
	allocated in the generic address space.
	</p>
	<p>
	The address space names without the __ prefix i.e. <code class="function">global</code>,
	<code class="function">local</code>, <code class="function">constant</code>
	and <code class="function">private</code>
	may be substituted for the corresponding address
	space names with the __ prefix.
	</p>
	<p>
	The address space name for arguments to a function
	in a program, or local variables of a function
	is <code class="function">__private</code>. All function
	arguments shall be in the <code class="function">__private</code> address space.
	The address space for a variable at program scope
	or a static variable inside a function can either
	be <code class="function">__global</code> or
	<code class="function">__constant</code>, but defaults to
	<code class="function">__global</code> if not specified.
	</p>
	<p>
	OpenCL 2.0 adds support for an unnamed <code class="function">generic</code>
	address space. Pointers that are declared
	without pointing to a named address space point to the
	<code class="function">generic</code> address space. Before
	referring to the region pointed to, the pointer
	must be associated with a named address space.
	Functions may be written with arguments and return values that point to the
	<code class="function">generic</code> address space.
	</p>
	<p>
	kernel function arguments declared to be a pointer or
	an array of a type must point to one of
	the named address spaces <code class="function">__global</code>,
	<code class="function">__local</code> or <code class="function">__constant</code>.
	</p>
	<p>
	The named address spaces are a subset of the generic
	address space except for the <code class="function">constant</code>
	address space.
	</p>
	<p>
	A pointer to address space A can only be assigned to
	a pointer to the same address space A or a
	pointer to the <code class="function">generic</code> address
	space. Casting a pointer to address space A to a pointer to
	address space B is illegal if A and B are named
	address spaces and A is not the same as B.
	</p>
	<p>
	The <code class="function">__global</code>, <code class="function">__constant</code>,
	<code class="function">__local</code>,
	<code class="function">__private</code>, <code class="function">__generic</code>,
	<code class="function">global</code>,
	<code class="function">constant</code>, <code class="function">local</code>, and
	<code class="function">private</code> names are reserved for use as address space
	qualifiers and shall not be used otherwise.
	The <code class="function">__generic</code> and <code class="function">generic</code>
	names are reserved for future use.
	</p>
	<p>
	The size of pointers to different address spaces
	may differ. It is not correct to assume
	that, for example, <code class="code">sizeof(__global int *)</code>
	always equals <code class="code">sizeof(__local int *)</code>.
	</p>
	</div>
	<div class="refsect2">
	<a id="example1"></a>
	<h3>
	Examples
	</h3>
	<p>
	General qualifier examples follow:
	</p>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left">
	// declares a pointer p in the private address space that
	// points to an object in address space global
	global int *p;

	void foo (...)
	{
	// declares an array of 4 floats in the private address space
	float x[4];
	...
	}
	</td>
	</tr>
	</tbody>
	</table>
	</div>
	<p>
	Example:
	</p>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left">
	private int f() { ... } // should generate an error
	local int *f() { ... } // allowed
	local int * private f() { ... }; // should generate an error.
	</td>
	</tr>
	</tbody>
	</table>
	</div>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left">
	global float4 *color; // An array of float4 elements
	typedef struct {
	float a[3];
	int b[2];
	} foo_t;
	global foo_t *my_info; // An array of foo_t elements.
	</td>
	</tr>
	</tbody>
	</table>
	</div>
	<p>
	</p>
	<div class="informaltable">
	<table class="informaltable" border="0">
	<colgroup>
	<col align="left" class="col1" />
	</colgroup>
	<tbody>
	<tr>
	<td align="left">
	global int foo; // OK.
	int foo; // OK. Declared in the global address space
	global uchar buf[512]; // OK.
	global int baz = 12; // OK. Initialization is allowed
	static global int bat; // OK. Internal linkage

	global uchar bigbuf[CL_DEVICE_MAX_GLOBAL_VARIABLE_SIZE]; // OK.

	static int foo; // OK. Declared in the global address space
	static global int foo; // OK.

	int *foo; // OK. foo is allocated in global address space.
	// pointer to foo in generic address space

	void func(...)
	{
	int *foo; // OK. foo is allocated in private address space.
	// foo points to a location in generic address space.
	...
	}

	global int * global ptr; // OK.
	int * global ptr; // OK.
	constant int *global ptr=&baz; // error since baz is in global address
	// space.
	global int * constant ptr = &baz; // OK

	// Pointers work. Also, initialization to a constant known at
	// program load time
	global int *global baz_ptr = &baz;

	global image2d_t im; // Error. Invalid type for program scope
	// variables

	global event_t ev; // Error. Invalid type for program scope variables

	global int *bad_ptr; // Error. No implicit address space
	</td>
	</tr>
	</tbody>
	</table>
	</div>
	</div>
	<div class="refsect1">
	<a id="specification"></a>
	<h2>Specification</h2>
	<p>
	<img src="pdficon_small1.gif" />

	<a href="https://www.khronos.org/registry/cl/specs/opencl-2.1-openclc.pdf#page=34" target="OpenCL Spec">OpenCL Specification</a>
	</p>
	</div>
	<div class="refsect1">
	<a id="seealso"></a>
	<h2>Also see</h2>
	<p>
	<a class="citerefentry" href="local.html"><span class="citerefentry"><span class="refentrytitle">__local</span></span></a>,
	<a class="citerefentry" href="constant.html"><span class="citerefentry"><span class="refentrytitle">__constant</span></span></a>,
	<a class="citerefentry" href="private.html"><span class="citerefentry"><span class="refentrytitle">__private</span></span></a>,
	<a class="citerefentry" href="qualifiers.html"><span class="citerefentry"><span class="refentrytitle">qualifiers</span></span></a>
	</p>
	</div>
	<div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2015 The Khronos Group Inc.
	Permission is hereby granted, free of charge, to any person obtaining a
	copy of this software and/or associated documentation files (the
	"Materials"), to deal in the Materials without restriction, including
	without limitation the rights to use, copy, modify, merge, publish,
	distribute, sublicense, and/or sell copies of the Materials, and to
	permit persons to whom the Materials are furnished to do so, subject to
	the condition that this copyright notice and permission notice shall be included
	in all copies or substantial portions of the Materials.
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